1. Field of the Invention
The present invention relates generally to the control of an internal combustion engine having an air introduction device in the engine device.
2. Background of the Invention
To reduce engine emissions, it is desirable to rapidly heat catalyst converters in the exhaust system. In other words, catalyst converters achieve higher emission reduction after they have reached a predetermined operating temperature. Thus, to lower vehicle emissions, various methods are available to raise catalyst temperature as fast as possible.
In one approach to raise the catalyst temperature, the engine is operated with a retarded ignition timing from the best timing in terms of torque generation. In this approach, an exhaust temperature from the combustion chamber is raised due to less expansion of the combusted gas from the retarded ignition timing in order to heat the catalyst converter. However, the inventors herein have recognized that this approach is becoming insufficient for increasing demand to rapidly heat the catalytic converter particularly during a small air-flow operation such as an idle condition.
In another approach to raise the catalyst temperature, the engine is operated with a rich air-fuel mixture while secondary air is provided directly into the exhaust system upstream the catalyst converter. Such a system is disclosed in U.S. Pat. No. 5,136,842. In this system, the excess fuel from the combustion chamber is exhausted into the exhaust pipe upstream of the catalyst converter and burnt with the secondary air. The burnt fuel upstream the catalyst converter generates heat to raise the catalyst temperature.
Although this system is able to rapidly raise the catalyst temperature while keeping the hydrocarbon emission low, the inventors herein have recognized that the excess fuel from the combustion chamber deteriorates the fuel economy since it does not contribute to the torque generation.
The inventors herein have further recognized that during larger airflow operation, the exhaust pressure rise limits the introduction of secondary air so that it is insufficient for exothermic reaction of the hydrocarbon to heat the catalytic converter.
The above disadvantages with prior approaches are overcome by a method for operating an engine with an emission control device in an exhaust system of the engine, and an air introduction device coupled to the engine exhaust system. The method comprises: in response to an indication that actual engine output is lower than a pre-selected value, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; and in response to an indication that actual engine output is equal to or greater than said pre-selected value, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture.
According to the first aspect of the present invention, the engine operation with the rich air-fuel mixture is terminated when the actual engine output is equal to or greater than the pre-selected value where the possible fuel economy deterioration and the possible exhaust emission deterioration resulting from the possible shortage of the secondary air are significant. At the same time, the engine operates with the retarded ignition timing and the lean air-fuel mixture so that the catalyst temperature rises rapidly because of increased air mass from the lean mixture and the engine produces less raw hydrocarbon because of the lean air/fuel ratio thereby avoiding the exhaust emission and fuel economy deterioration.
In a second aspect of the present invention, the method comprises: in response to an indication that an actual engine output is smaller than a pre-selected value and an exhaust temperature is lower than a pre-selected threshold, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; in response to an indication that the actual engine output is equal to or greater than said pre-selected value and the exhaust temperature is lower than said pre-selected threshold, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture; and in response to an indication that the exhaust temperature is equal to or higher than said pre-selected threshold, operating the engine to combust a stoichiometric air-fuel mixture.
In accordance with the second aspect of the invention, in addition to the first aspect, the engine operates with the stoichiometric air-fuel ratio when the exhaust temperature is equal to or higher than the pre-selected temperature so that exhaust emission is optimally reduced when the catalyst temperature increase is unnecessary.
In a third aspect of the present invention, the method comprises: in response to an indication that the engine is in an idle condition, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; and in response to an indication that the engine is in a non-idle condition, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture.
According to the third aspect of the present invention, the engine operation with the rich air-fuel mixture is terminated when the engine operates at the non-idle condition where the possible fuel economy deterioration and the possible exhaust emission deterioration resulting from the possible shortage of the secondary air are significant. At the same time, the engine operates with the retarded ignition timing and the lean air-fuel mixture so that the catalyst temperature rises rapidly because of increased air mass from the lean mixture and the engine produces less raw hydrocarbon because of the lean air/fuel ratio thereby avoiding the exhaust emission and fuel economy deterioration.
In a fourth aspect of the present invention, the method comprises: in response to an indication that the engine is in an idle condition and an exhaust temperature is lower than a pre-selected threshold, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; in response to an indication that the engine is in a non-idle condition and the exhaust temperature is lower than said pre-selected threshold, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture; and in response to an indication that the exhaust temperature is equal to or higher than said pre-selected threshold, operating the engine to combust a substantially stoichiometric air-fuel mixture.
In accordance with the fourth aspect of the invention, in addition to the third aspect, the engine operates with the stoichiometric air-fuel ratio when the exhaust temperature is equal to or higher than the pre-selected temperature so that exhaust emission is optimally reduced when the catalyst temperature increase is unnecessary.
In a fifth aspect of the present invention, the method comprises: in response to an indication that an engine airflow is smaller than a pre-selected value, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; and in response to an indication that the engine airflow is equal to or greater than said pre-selected value, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture.
According to the fifth aspect of the present invention, the engine operation with the rich air-fuel mixture is terminated when the engine airflow is equal to or greater than the pre-selected value where the possible fuel economy deterioration and the possible exhaust emission deterioration resulting from the possible shortage of the secondary air are significant. At the same time, the engine operates with the retarded ignition timing and the lean air-fuel mixture so that the catalyst temperature rises rapidly because of increased air mass from the lean mixture and the engine produces less raw hydrocarbon because of the lean air/fuel ratio thereby avoiding the exhaust emission and fuel economy deterioration.
In a sixth aspect of the present invention, the method comprises: in response to an indication that an engine airflow is smaller than a pre-selected value and an exhaust temperature is lower than a pre-selected threshold, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; in response to an indication that the engine airflow is equal to or greater than said pre-selected value and the exhaust temperature is lower than said pre-selected threshold, operating the engine with ignition timing retarded from optimal timing to combust a lean air-fuel mixture; and in response to an indication that the exhaust temperature is equal to or higher than said pre-selected threshold, operating the engine to combust a stoichiometric air-fuel mixture.
According to the sixth aspect of the present invention, in addition to the fifth aspect, the engine operates with the stoichiometric air-fuel ratio when the exhaust temperature is equal to or higher than the pre-selected temperature so that exhaust emission is optimally reduced when the catalyst temperature increase is unnecessary.
In a seventh aspect of the present invention, the method comprises: in response to an indication that actual engine output is lower than a pre-selected value, operating the engine to combust a rich air-fuel mixture and adding air via the air introduction device; and in response to an indication that actual engine output is equal to or greater than said pre-selected value, operating the engine to combust a lean air-fuel mixture.
According to the seventh aspect of the present invention, the engine operation with the rich air-fuel mixture is terminated when the actual engine output is equal to or greater than the pre-selected value where the possible fuel economy deterioration and the possible exhaust emission deterioration resulting from the possible shortage of the secondary air are significant. At the same time, the engine operates the lean air-fuel mixture so that the engine produces less raw hydrocarbon because of the lean air/fuel ratio thereby avoiding the exhaust emission and fuel economy deterioration.
In this invention, by measuring a mass airflow into the engine, the actual engine output or the engine airflow is detected.
In this invention, the indication that the engine is in the idle condition may be generated by measuring a position of throttle valve throttling an airflow into the engine or by monitoring whether the engine is in engine idle speed control.
In this invention, the rich air-fuel mixture may be richer than 12:1, the air introduction device may be an air pump, a voltage applied to the pup may be adjusted to control an amount of air added via the pump, the amount of the air added via the pump may be determined based on exterior condition, more preferably including at least atmospheric pressure and temperature, the rich air-fuel ratio may be adjusted based on an amount of air added via the air introduction device, or air entering the engine may be adjusted when transitioning from the lean operation to the rich operation.
In the second, fourth, or sixth aspect of the invention, the pre-selected threshold is preferably a catalyst light-off temperature so that the catalyst optimally purifies the stoichiometric air-fuel mixture.